I was incorrect: It appears that you do in fact need root to run startx now:
(quoting the faq page for upgrade65):
Xorg(1). The Xorg binary is no longer installed setuid, so startx(1) can no longer be used by non-root users. The xenodm(1) display manager has to be used instead.
(quoting the faq page for upgrade65):
Xorg(1). The Xorg binary is no longer installed setuid, so startx(1) can no longer be used by non-root users. The xenodm(1) display manager has to be used instead.